Combination catalytic hydrocracking, pyrolytic cracking and catalytic reforming process for converting a wide boiling range crude hydrocarbon feedstock into various valuable products



United States Patent O1 hee 3,409,540 COMBINATION CATALYTIC HYDROCRACK-ING, PYROLYTIC 'CRACKING AND 'CATA- LYTIC REFORMING PROCESS FOR CON-VERTING A WIDE BOILING RANGE CRUDE HYDROCARBON FEEDSTOCK INTO VARI- OUSVALUABLE PRODUCTS George D. Gould, Orinda, Norman J. Paterson, SanRafael, and Ronald R. Roselius, Point Richmond, Calif., assignors toChevron Research Company, San Francisco, Calif., a corporation ofDelaware Filed Dec. 22, 1966, Ser. No. 603,917 4 Claims. (Cl. 20S-79)ABSTRACT OF THE DISCLOSURE A process for converting a wide boiling rangecrude petroleum feedstock into various valuable products includingethylene and aromatic hydrocarbons, comprising fracti-onating the crude,catalytically reforming a heavy straight run fraction thereof,catalytically hydrocracking a fraction thereof boiling in the range 350to 800 F., and pyrolytically cracking a light straight run fractionthereof together with a portion of the eluent from the hydrocrackingzone.

Background of invention (1) Field of invention.-The invention claimedherein is a combination process for converting a wide boiling rangecrude petroleum feedstock into various products including ethylene andaromatic hydrocarbons, using steps including catalytic reforming,pyrolytic cracking and catalytic hydrocracking.

(2) Description of prior art.-Heretofore it has been known to convert anaphtha feedstock pyrolytically to various products including ethylene.Such a process is disclosed in U.S. Patent 3,281,351. Heretofore it alsohas been known to fractionate a wide boiling range crude petroleum stockand to pyrolytically convert a lighter fraction thereof to variousproducts including ethylene. Such a process is disclosed in U.S. Patent3,060,116. In the former process the boiling range of the feedstock islimited, In the latter process the feedstock boiling range limitation isremoved, and a wide boiling range crude petroleum stock is processed;however, the straight run ygas oil and residual portions of thefeedstock are converted by catalytic cracking and thermal cracking,respectively. Catalytic cracking f the gas oil results in acatalytically cracked gasoline that would be a generally unsatisfactoryfeed for a pyrolytic cracking zone because of its high content ofisoparains. This catalytically cracked gasoline also would be anunsatisfactory feed for a catalytic reformer because of its high olefincontent. Thermal cracking of the residual portion produces a lightthermally cracked gasoline and a heavy thermally cracked gasoline. Theheavy thermally cracked gasoline, while suitable as a feed for acatalytic reformer, is produced in low yields.

By-product hydrogen produced in the foregoing types of prior artethylene manufacturing processes is largely wasted by being dissipatedas a fuel gas component.

In view of the foregoing, a useful technological improvement over theprocess of U.S. Patent 3,060,116, which by utilizing a full boilingrange crude feedstock is itself an improvement over the process of U.S.Patent 3,281,351, would be contributed to the art by a process thatwould accomplish the following purposes without increasing thethroughput of the crude feedstock:

(a) Decrease production of less valuable fuel oil, fuel gas and naphtha;

3,409,540 Patented Nov. 5, 1968 (b) Increase yield of more valuableethylene and butadiene;

(c) Increase yield of manufactured reformer feedstock;

(d) Increase quality of manufactured reformer feedstock;

(e) Produce other more valuable products including benzene and xylenes;

(f) By increasing yield of manufactured reformer feedstock, release somestraight run naphtha reformer feedstock for use as pyrolytic crackingzone feedstock, thereby increasing production of low boiling oleins,pyrolysis naphtha and carbon black feedstock and pitch binder oil;

(g) Incorporate into higher value liquid fuel products the hydrogendissipated as a fuel gas component in prior art processes, therebyincreasing both yield and quality of said liquid fuel products;

(h) Permit operation of entire system in hydrogen balance, that is, withthe hydrogen requirements of the entire system supplied by hydrogenproduced in the system.

It is an object of the present invention to provide a process that willaccomplish the foregoing purposes.

Statement of invention In accordance with one embodiment of the presentinvention there is provided an integrated hydrocarbon conversion processfor converting a crude hydrocarbon feedstock, boiling in the range C5 to1400 F., containing substantial quantities of materials boiling in therange C5 to 430 F. and substantial quantities of materials boiling inthe range 350 to 800 F., and having an API gravity in the range 20 to60, into various valuable products including ethylene and aromatichydrocarbons, which comprises:

(a) separating said feedstock into fractions, including a first fractionboiling below 400 F., a second fraction boiling below 430 F., and athird fraction boiling in the range 350 to 800 F., a substantial portionof the materials in said first fraction boiling below the boiling rangeof said second fraction, and a substantial portion of the materials insaid second fraction boiling above the boiling range of said firstfraction;

(b) catalytically hydrocracking said third fraction in a catalytichydrocracking zone;

(c) catalytically reforming in a catalytic reforming zone -said secondfraction and a portion of the effluent from said hydrocracking zone;

(d) pyrolytically cracking in a pyrolytic cracking zone said rstfraction and a portion of the effluent from said hydrocracking zone; and

(e) recovering as products ethylene from the eflluent from saidpyrolytic cracking zone and'aromatic hydrocarbons from the efliuent fromsaid catalytic reforming zone.

In accordance with another embodiment of the present invention saidcatalytic hydrocracking zone is supplied with hydrogen from saidcatalytic reforming zone and with hydrogen separated from the effluentfrom said pyrolytic cracking zone.

In accordance with another embodiment of the present invention there isrecycled to said hydrocracking zone from the efliuent thereof a fractionboiling in the range 350 to 800 F.

In accordance with another embodiment of the present invention saidthird fraction boils in the range 450 to 750 F., the portion of theeffluent from said hydrocracking zone that is pyrolytically cracked insaid pyrolytic cracking zone boils below 450 F. and the portion of theeffluent from said catalytic hydrocracking zone that is reformed in saidcatalytic reforming zone boils below 430 F.

Advantages of the invention The advantages of the process of the presentinvention, compared with prior art processes such as the process of U.S.Patent 3,060,116, include accomplishment of the purposes set forth abovein connection with Description of Prior Art. It will be noted that, inaccomplishing those purposes, advantage is taken of these facts anddiscoveries:

(a) As the end point of the feed to the pyrolytic cracking zone rises,the yield of ethylene, based on the feed, decreases. In the process ofthe present invention the permissible end point of the feed to thepyrolytic cracking zone is higher than in the process of U.S. Patent3,281,351 or 3,060,116. Accordingly, a smaller yield of ethylene isobtained as a result of pyrolytically cracking the heavier materials notpreviously sent to the pyrolytic cracking zone, based on the total feedto that zone. However, because those heavier materials are sent to thatzone in addition to the lighter straight run materials heretoforecracked in that zone, that is, because the throughput of those lighterstraight run materials being fed to that zone is not decreased, there isa greater production of ethylene from that zone on an absolute basis.

(b) The heavier straight run materials that may be sent to the pyrolyticcracking zone in the process of the present invention were sent inprevious processes to the reforming zone. These heavier straight runmaterials have a low naphthene content, and therefore are not an idealreformer feed. They have a high normal paraffin content, however, andtherefore constitute an excellent feed for the pyrolytic cracking zone.

(c) The heavier straight run materials diverted from the reforming zoneand sent to the pyrolytic cracking zone in the process of the presentinvention are replaced with a manufactured reformer feedstock, namely aportion of the efuent from the hydrocracking zone. This portion of theeffluent from the hydrocracking zone has a higher naphthene content thanthe straight run materials it replaces as reformer feedstock, andtherefore is a more desirable reformer feedstock.

(d) The catalytic reforming zone in the process of the presentinvention, supplied with a higher quality reformer feedstock than inprocesses such as that of U.S. Patent 3,060,116, produces a reformatefrom which valuable aromatic hydrocarbons can be extracted. From theremaining portion of the reformate, additional quantities of pyrolyticcracking zone feedstock, desirably rich in normal parains, is obtained.

Further advantages of the process of the present invention will beapparent from the following description.

Drawing The accompanying drawing illustrates an embodiment of processunits and ow paths suitable for carrying out the process of the presentinvention.

Description of a preferred embodiment The preferred embodiment of theprocess of the present invention that is illustrated in the accompanyingdrawing will now be discussed.

Referring now to the drawing, a crude hydrocarbon feed is passed throughline 1 to crude distillation column 2. The crude hydrocarbon feed mayhave an extremely wide boiling range, for example C1 to l200 F. orwider. It contains substantial quantities of materials boiling in theranges C to 430 F. and 350 to 800 F. It has an API gravity in the rangeto 60, preferably 35 to 45. Examples of suitable crude feeds are MiddleEast, African, North American and South American petroleum crude oilshaving the foregoing characteristics.

In crude distillation column 2, the crude feed is separated into: a C1-fraction, withdrawn through line 3; a C2 to 150 F. fraction, passedthrough line 4 to pyrolytic cracking zone 5; a 150 to 300 F. fraction,passed through line 6 to reforming zone 7; a 300 to 450 F fraction,passed through lines 8 and 4 to pyrolytic cracking zone 5; a 450 to 750F. fraction, passed through line 9 to hydrocracking zone 10; and a 750F.{fuel oil fraction, withdrawn through line 15. The fuel oil withdrawnthrough line 15 may be burned to supply all or a portion of the thermalenergy requirements of the system. All or a portion of that fuel oil maybe passed to a conventional thermal cracker or to another hydrocrackingzone for further processing. However, it is preferred to minimize theproduction of the fuel oil and to use it as such rather than subjectingit to further processing.

A portion of the 150 to 300 F. fraction in line 6 may be passed throughlines 16 and 4 to pyrolytic cracking zone 5 if desired.

Pyrolytic cracking zone 5 is a conventional high temperature crackingzone, operating at temperatures in the range of about 1200 to 18010" F.or higher and preferably 1400" to 1600 F., at pressures of 0 to 50p.s.i.g. and residence periods at reaction temperatures in the range of0.1 to 3 seconds and preferably 0.6 to 1.3 seconds. The pyrolyticcracking zone preferably is operated as a thermal cracker, that is, inthe absence of catalysts. However, it is within the purview of theprocess of the present invention for the pyrolytic cracking zone tocontain suitable cracking catalysts, for example, silica-aluminacatalysts or mixtures of cracking and dehydrogenation catalysts. Whenoperated in the absence of catalysts the pyrolytic cracking zonepreferably is operated with the addition of steam to the zone, theamount of steam added ranging broadly from 30 to 150 percent andpreferably from 75 to percent by weight of the hydrocarbon feed.Alternatively, the pyrolytic cracking zone may be operated in accordancewith the conventional Wulff process, that is, at the aforesaid hightemperatures and low pressures but in the absence of steam. In anyevent, the pyrolytic cracking zone effects conversion of the feedthereto to a cracked product rich in gaseous olens and also containingdiolefins, aromatics and other products. When pyrolytic cracking zone 5is operated as a steam cracker, steam may be introduced thereto throughline 17.

Hydrocracking zone 10 is a conventional hydrocracking zone supplied withhydrogen through line 18.

The catalyst employed in hydrocracking zone 10 comprises an activecracking catalyst component and at least onehydrogenating-dehydrogenating component. The cracking component maycomprise any one or more of such acidic materials as silica-alumina,silica-magnesia, silica-alumina-zirconia, alumina-boria, variousacid-treated clays and similar materials. Particularly preferredcatalyst cracking components are synthetically prepared silicaaluminacompositions having a silica content in the range of from about 15 to 99percent by weight and an alumina content in the range of from about 1 to85 percent by weight. The hydrogenating-dehydrogenating components ofthe catalyst can be selected from any one or more of vthe various GroupsV, VI, VII and VIII metals, as well as from the oxides and sulfidesthereof alone or together with promoters or stabilizers that may have bythemselves small catalytic effect. Especially suitable catalystsinclude:

(a) Nickel or a compound thereof in association with silica-alumina;

(b) Nickel or a compound thereof and either tungsten or a compoundthereof or molybdenum or a compound thereof in association withsilica-alumina.

The amount of hydrogenating-dehydrogenating components present may bevaried within relatively wide limits of from about 0.5 to 30 percentbased on the weight of the entire catalyst.

Hydrocracking zone 10 is supplied with at least 1,500 s.c.f. of hydrogenper barrel of feed thereto. At least 500, and normally from about 1,000to 2,000 s.c.f. of hydrogen are consumed in zone 10 per barrel of feedthereto that is converted to synthetic products-ie., to products boilingbelow the initial boiling point of said feed. While operat1on of theprocess of the present invention in the integrated manner disclosedherein can readily be accomplished in hydrogen balance so that hydrogensupplied from extraneous sources need not be resorted to, extraneoushydrogen nevertheless may be supplied to zone through line 19 ifdesired.

Hydrocracking zone 10 is operated at a temperature of 400 to 900 F.,preferably 550 to 750 F., a pressure of 500 to 3,500 p.s.i.g.,preferably 1,000 to 1,500 p.s.i.g., and an LHSV from 0.1 to 15,preferably 0.5 to 5.0. Under these conditions, the feed is converted inamounts exceeding 20 percent per pass to synthetic materials-ie.,materials boiling below the initial boiling point of the feed. Thereactions that occur in zone 10 include hydrocracking and isomerizationand result in the production of significant quantities of low-boiling,normal parains, valuable as feedstock components for pyrolytic crackingzone 5, significant quantities of normal butane and isobutane, valuablefor purposes hereinafter discussed, signicant quantities of a valuablefeedstock for catalytic reforming zone 7 and a normally liquid fractionboiling below 450 F., valuable as an additonal feedstock for pyrolyticcracking zone 5.

The etlluent from hydrocracking zone 10 is passed through line 20 toseparation zone 25. From separation zone 25, a hydrogen stream isrecycled to hydrocracking zone 10 through lines 26 and 18, and a fuelgas fraction and an isopentane fraction are withdrawn as productsthrough lines 27 and 28, respectively. From separation zone 25, anethane fraction, a propane fraction, a normal propane fraction, a normalhexane fraction, a normal isohexane fraction and a fraction boiling inthe range 300 to 450 F. are passed through lines 29 to 34, respectively,and thence through lines and 4 to pyrolytic cracking zone 5.

From separation zone 25, a normal butane fraction is passed through lineand thence through line 41 for recovery as a product. Alternatively, allor a portion of the normal butane fraction in line 40 may be passedthrough lines 42 and 43 to isomerization zone 44. From separation zone25, an isobutane fraction is passed through lines 45, 46 and 47 toalkylation zone 48. From separation zone 25, a fraction boiling in therange C7 to 300 F. is passed through lines 49 and 6 to reforming zone 7.From separation zone 25, a bottoms fraction boiling above 450 F. isrecycled through lines 50 and 9 to hydrocracking zone 10.

Reforming zone 7 is a conventional catalytic reforming zone containing asuitable reforming catalyst having dehydrogenation or aromatizationactivity, particularly an activity for promoting aromatization ofnaphthenes to aromatics and desirably for aromatization for paratlnichydrocarbons to aromatics through a dehydrocyclization reaction.Examples of suitable catalysts are Group VI metal suldes or oxides, suchas the oxides or sulfides of molybdenum, chromium or tungsten, ormixtures thereof, on suitable carriers, such as activated alumina,bauxite,

zinc, aluminate or the like. A preferred reforming catalyst comprisesabout 0.3 to 1.5 percent by weight platinum or palladium associated witha carrier material, such as alumina or silica-alumina. Reforming zone 7is operated at a temperature of 850 to 1,050f F., preferably 875 to1,000 F., a pressure of 50 to 1,500 p.s.i.g., preferably 100 to 700p.s.i.g., a space velocity of 0.5 to 10, preferably 0.5 to 3, volumes ofliquid oil feed per hour per volume of catalyst, and ahydrogen-to-hydrocarbon mol ratio of 2 to 20, preferably 4 to 10.Hydrogen may be supplied to reforming zone 7 through line 55 and maycomprise hydrogen recycled through line 56, hydrogen supplied throughline 57, or both.

The effluent from reforming zone 7 is passed through line 58 toseparation zone 59. From separation zone 59, hydrogen is recycled toreforming zone 7 through lines 60, 56 and 55 and also is passed throughlines 60, 61, 62 and 18 to hydrocracking zone 10. From separation zone59 a fuel gas fraction and an isopentane fraction are withdrawn asproducts through lines 68 `and 69, respectively.

From separation zone 59, an ethane fraction, a propane fraction, anormal pentane fraction, a normal hexane fraction and an isohexanefraction are passed through lines 70 to 74, respectively, and thencethrough lines 75, 35 and 4 to pyrolytic cracking zone 5.

From separation zone 59, aromatic product fractionsnamely, benzene,xylenes and C94- aromatics-are withdrawn through lines to 82,respectively. From separation zone 59, a toluene fraction is passedthrough line 83 to conventional dealkylation zone 84 where it isdealkylated, in the presence of hydrogen supplied through line 85, toproduce benzene. The effluent from dealkylation zone 85 is passedthrough line 90 to separation zone 91 from which fuel gas and benzenefractions are withdrawn through lines 92 and 93, respectively. Fromseparation zone 59, a fraction boiling in the range of 400 to 475 F.,comprising methyl naphthalenes, is passed through line 94 to:conventional dealkylation zone 95 where it is subjected to dealkylationconditions in the presence of hydrogen supplied through line 96. Theellluent from dealkylation zone 95 is passed through line 97 toseparation zone 98 from which a fuel gas fraction and naphthalenefraction are withdrawn through lines 99 and 100, respectively.

From separation zone 59, a normal butane fraction is passed through line106 and thence through line 107 as a produ-ct. Alternatively, all or aportion thereof may be passed through lines 108 and 43 to isomerizationzone 44. From separation zone 59, an isobutane fraction is passedthrough lines 109, 46 and 47 to alkylation zone 48.

Isomerization zone 44 is a conventional isomerization zone in which thenormal butane supplied thereto through line 43 is isomerized toisobutane which is passed through lines 110, 46 and 47 to alkylationzone 48.

The effluent from pyrolytic cracking zone 5 is passed through line toseparation zone 116. From separation zone 116, a C1- fraction is passedthrough line 117 to conventional hydrogen separation zone 118. Theetlluent from separation zone 118 is passed through line 119 toseparation zone 120 from which a fuel gas fraction is withdrawn throughline 121 and from which hydrogen is passed to hydrocracking zone 10through lines 122, 62 and 18. From separation zone 116, an ethylenefraction is withdrawn as a product through line 123. From separationzone 116, a propylene fraction is passed through line 124 toconventional disproportionation zone 125. The effluent from zone 125 ispassed through line 126 to separation zone 127 from which an ethylenefraction is passed through line 128 to line 123 and from which abutylene fraction is passed through lines 129 and 130 to dehydrogenationzone 131. From separation zone 116, a butylene fraction is passedthrough line 130 to dehydrogenation zone 131. From separation zone 116,a butadiene product fraction is withdrawn through line 140. Fromseparation zone 116, a pyrolysis naphtha fraction, boiling generally inthe range C5 to 450 F. and containing a high percentage of aromatics, ispassed through line 141 to conventional hydrogenation zone 142. In zone142, C6 and C7 diolens in the pyrolysis naphtha are selectivelyhydrogenated in the presence of hydrogen supplied to zone 142 throughline 143. The eilluent from hydrogenation zone 142, still containing ahigh percentage of aromatics, is passed through lines 144 and 58 toseparation zone 59 where it is separated into fractions previouslydiscussed which are withdrawn from separation zone 59 as previouslydiscussed. From separation zone 116, a bottoms product fraction usefulas a carbon black feedstock and pitch binder oil is withdrawn throughline 150.

Dehydrogenation zone 131 is a conventional dehydrogenation zoneemploying any of a wide variety of known dehydrogenation catalysts ofwhich the commercially available chromia-on-alumina catalyst containingabout 20 weight percent Cr203 is a typical and suitable embodiment.Operating conditions may include temperatures from about 950 to 1,200F., preferably 1,000 to 1,100 F., relatively low pressures, generallyatmospheric or subatmospheric, and 0.5 to 2.1 volumes of charge pervolume of catalyst per hour. In dehydrogenation zone 131, the butylenefeed is dehydrogenated to produce butadiene. The eiuent fromdehydrogenation zone 131 is passed through line 160 to separation zone161 from which hydrogen is recycled to hydrocracking zone 10 throughlines 62 and 18 and from which butadiene is recovered through line 162.

A portion of the butylene in line 130 is passed through lines 170 and 47to alkylation zone 48. Alkylation zone 48 is a conventional alkylationzone in which the isobutane and butylene feeds thereto are reactedtogether under conventional alkylation conditions to produce to alkylateproduct which is withdrawn from zone 48 through line 171.

If desired, a portion of the butylene in line 170 may be passed throughline 172 lto conventional polymerization zone 173. This is a convenientmanner of utilizing butylenes which are produced in excess of the amountfor which there is isobutane available for -alkylation and, therefore,is a convenient way from maintaining isobutane balance in the system.Conventional polymerization zone 173 may be, for example, a bulk liquidacid polymerization zone supplied with liquid phosphoric acid throughline 174. The acid may have a concentration of from about 117 to 122percent. Polymerization zone 173 may be operated at a temperature offrom about 175 to 300 F., -a pressure of from about 200 to 1,800p.s.i.g. and a space velocity in excess of about 0.2 volume ofhydrocarbon per volume of acid per hour. From zone 173, a motor polymerproduct is withdrawn through line 175. Acid from the eiuent in line 175is recycled to zone 173 after having been separated in anacid-hydrocarbon settler, which is not shown.

The foregoing detailed description will be further appreciated from aconsideration of the following additional points:

(1) The isopentane that is recovered from separation zones 25 and 59 maybe used as a gasoline blend stock;

(2) The Cg-iaromatic fraction recovered from separation zone 59 may beused to make various valuable products, such as durene or pseudocumeneor used as a gasoline blend stock;

(3) If desired, LPG (C3-|-nC4-l-z'C4) may be recovered as a product fromseparation zone 25 or separation zone 59, or both;

(4) If desired, 5 to 15 weight percent of colloidal carbon black may beadded to the carbon black feedstock and pitch binder oil recovered fromseparation zones 59 and 116 to aid the recovered oil in meeting thespecifications for pitch binder oil; and

(5) The separation of aromatics from the other components of theefliuentl from reforming zone 7, that is accomplished in separation zoneV59, may be accomplished by steps including a conventional aromaticextraction step.

From the foregoing, it may be seen that with the process of the presentinvention there may be produced from a barrel of crude a variety ofvaluable products, including ethylene, butadiene, carbon black and pitchbinder oil, benzene and xylenes. It may be seen that the process enablesthese results to be obtained with a self-contained operation in whichall necessary hydrogen for the operation is produced internally, therebyobviating the need for an external source of hydrogen. The processresults in the production, from a low-grade crude fraction, of ahigh-quality reformer feedstock having a high aromatic and isoparaincontent. The 450 to 750 F. portion of the original crude feedstock, thatheretofore has been of little use except as furnace oil or a bunker fuelblend stock, is converted in the hydrocracking zone to lower boiling andmore valuable products and to quality feedstocks for the otherconversion units in the combined processing scheme.

Although only specific arrangements and modes of operation of thepresent invention have been described and illustrated, numerous changescan be made in those arrangements and modes without departing from thespirit of the invention, and all such changes that fall within the scopeof the appended claims are intended to be embraced thereby.

What is claimed is:

1. An integrated hydrocarbon conversion process for converting a crudehydrocarbon feedstock, boiling in the range C5 to 1400 F., containingsubstantial quantities of materials boiling in the range C5 to 430 F.and substantial quantities of materials lboiling in the range 350 to 800F., and having an API gravity in the range 20 to 60, into variousvaluable products including ethylene and aromatic hydrocarbons, whichcomprises:

(a) separating said feedstock into fractions, including a first fractionboiling below 400 F., a second fraction boiling -below 430 F., and athird fraction boiling in the range 350 to 800 F., a substantial portionof the materials in said first fraction boiling below the lboiling rangeof said second fraction, and a substantial portion of the materials insaid second fraction boiling above the boiling range of said firstfraction;

(b) catalytically hydrocracking said third fraction in a catalytichydrocracking zone;

(c) catalytically reforming in a catalytic reforming zone said secondfraction and a portion of the efuent from said hydrocracking zone;

(d) pyrolytically cracking in a pyrolytic cracking zone said lfirstfraction and a portion of the efliuent from said hydrocracking zone; and

(e) recovering as products ethylene from the ei'lluent from saidpyrolytic cracking zone and aromatic hydrocarbons from theefuent fromsaid catalytic reforming zone.

2. A process as in claim 1, wherein said catalytic hydrocracking zone issupplied with hydrogen from said catalytic reforming zone and withhydrogen separated from the efiiuent from said pyrolytic cracking zone.

3. A process as in claim 1, wherein there is recycled to said catalytic'hydrocracking zone from the effluent thereof a fraction boiling in therange y350" to 800 F.

4. A process as in claim 1, wherein said third fraction boils in therange 450 to 750 F., wherein the portion of the eluent from saidcatalytic hydrocracking zone that is pyrolytically cracked in saidpyrolytic cracking zone boils below 450 F., and wherein the portion ofthe eluent from said catalytic hydrocracking zone that is reformed insaid catalytic reforming zone boils below 430 F.

References Cited UNITED STATES PATENTS 2,973,313 2/1961 Pevere et al.208--93 3,060,116 I10/1962 Hardin et al. 208--93 3,281,350 10/1966 Codetet al 208-93 3,281,351 10/1966 Gilliland et al. 208-93 OTHER REFERENCESVoorhies et al.: Advances in Petroleum Chemistry and Refining, vol.VIII, pp. 171-172, 1964, copy in art unit 116, Pub. IntersciencePublishers, N.Y.

DELBERT E. GANTZ, Primary Examiner.

H. LEVINE, Assistant Examiner.

